Tropical Storm PRAPIROON Advisory Sa, 09.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (PRAPIROON) WARNING
NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 22W (PRAPIROON), LOCATED APPROXIMATELY 585 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WESTWARD
AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY SHOWS DEEP CONVECTIVE BANDING STEADILY
DEVELOPING ALONG THE SOUTHERN HALF OF THE SYSTEM. A 081453Z OSCAT
PASS AND A PREVIOUS 081236Z ASCAT PASS BOTH INDICATED THE LOW LEVEL
CIRCULATION CENTER (LLCC) IS LOCATED SLIGHTLY SOUTH OF THE CENTRAL
DEEP CONVECTION. THE CURRENT POSITION TAKES THIS INTO ACCOUNT AND IS
BASED ON THE OSCAT PASS AND THE FIX FROM PGTW. THE CURRENT INTENSITY
IS BASED ON A CONSOLIDATION OF DVORAK FIXES RANGING FROM 55 TO 65
KNOTS FROM PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES GOOD
RADIAL OUTFLOW ASSOCIATED WITH A POINT SOURCE ANTICYCLONE DEVELOPING
OVER THE LLCC IN A LOW VERTICAL WIND SHEAR (VWS) ENVIRONMENT (05 TO
10 KNOTS). TS 22W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A MID
TO UPPER LEVEL SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS PRAPIROON IS FORECAST TO CONTINUE ON A GENERAL WESTWARD
TRACK FOR THE NEXT 12 HOURS BUT WILL START MOVING MORE NORTHWARD AS
IT REACHES THE WESTERN EXTENT OF THE STR, WHICH WILL BEGIN TO ERODE
AS A SHORTWAVE TROUGH OUT OF EASTERN CHINA DIGS TO THE NORTH OF THE
SYSTEM. THE TRACK SPEEDS WILL SLOW AS THE STRENGTH OF THE STR
DIMINISHES. BETWEEN TAU 48 AND 72 TS 22W WILL TRANSITION TO A
NORTHWARD TRACK AROUND THE WESTERN EXTENT OF THE STR. FAVORABLE
UPPER LEVEL AND LOW LEVEL ENVIRONMENTS WILL ALLOW TS 22W TO
INTENSIFY THROUGH TAU 72.
   C. IN THE EXTENDED TAUS, TS 22W IS FORECAST TO TRACK
NORTHEASTWARD AS A BUILDING NEAR EQUATORIAL RIDGE LINKS WITH THE STR
CAUSING THE STR TO REORIENT NORTHEAST TO SOUTHWEST. A SLIGHT
DECREASE IN SEA SURFACE TEMPERATURES AND A SLIGHT INCREASE IN VWS
WILL SLIGHTLY WEAKEN THE SYSTEM IN THE EXTENDED TAUS. HOWEVER, THE
ENVIRONMENT WILL REMAIN FAVORABLE FOR THE SUSTAINMENT OF THE SYSTEM
BEYOND THE FORECAST PERIOD. MODEL GUIDANCE HAS COME INTO BETTER
AGREEMENT ON THE RECURVATURE OF THE SYSTEM, BUT VARIES WIDELY IN THE
TIMING AND SPEED. THE CURRENT FORECAST IS WEST OF THE CONSENSUS AND
FOLLOWS MORE CLOSELY WITH EMCF AND GFS. NGPS, WBAR, EGRR, AND GFDN
RECURVE THE SYSTEM MORE QUICKLY (WITHIN THE NEXT 12 TO 24 HOURS).
BASED ON THE CURRENT TRACK SPEED AND DIRECTION, AN EARLY SHIFT
NORTHWARD SEEMS UNLIKELY. THE CONFIDENCE IN THE FORECAST REMAINS
LOW, BASED ON THE WIDE VARIATION IN MODEL GUIDANCE.//
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